Fix bug #3022 (Closing Find bar with many results is very slow) -- Add
operation() wrapper to clearHighlights() to guarantee it runs in a CM
rendering batch no matter where it's called from. Also simplify one caller
that didn't need to use getSearchState().
Merge pull request #3076 from adobe/pflynn/batch-find-highlighting

Fix bug #3022 (Closing Find bar with many results is very slow)